Surface relaxation of topological insulators: Influence on the electronic structure

The surface structure of topological insulators Bi2Te3(111) and a single bilayer bismuth on it was studied by low-energy electron-diffraction analysis. The topmost quintuple layer of Bi2Te3 showed only a slight relaxation (similar to 1% contraction). On the other hand, the bilayer Bi was strongly distorted compared to bulk Bi (3.5% in-plane contraction and similar to 7% out-of-plane expansion). First-principles calculation reveals that this distortion has a large influence on the electronic structure and can enlarge the band gap.